Robert Goulston Gilbert (born 1946) is a polymer chemist

Polymer chemistry

Polymer chemistry or macromolecular chemistry is a multidisciplinary science that deals with the chemical synthesis and chemical properties of polymers or macromolecules. According to IUPAC recommendations, macromolecules refer to the individual molecular chains and are the domain of chemistry...

 whose most significant contributions have been in the field of emulsion polymerisation

Emulsion polymerization

Emulsion polymerization is a type of radical polymerization that usually starts with an emulsion incorporating water, monomer, and surfactant. The most common type of emulsion polymerization is an oil-in-water emulsion, in which droplets of monomer are emulsified in a continuous phase of water...

. In 1970, he gained his PhD from the Australian National University

Australian National University

The Australian National University is a teaching and research university located in the Australian capital, Canberra.As of 2009, the ANU employs 3,945 administrative staff who teach approximately 10,000 undergraduates, and 7,500 postgraduate students...

, and worked at the University of Sydney

University of Sydney

The University of Sydney is a public university located in Sydney, New South Wales. The main campus spreads across the suburbs of Camperdown and Darlington on the southwestern outskirts of the Sydney CBD. Founded in 1850, it is the oldest university in Australia and Oceania...

 from then until 2006. In 1982, he was elected a fellow of the Royal Australian Chemical Institute

Royal Australian Chemical Institute

The Royal Australian Chemical Institute Inc. is both the qualifying body in Australia for professional chemists and a learned society promoting the science and practice of chemistry in all its branches. The RACI hosts conferences, seminars and workshops...

; in 1994, he was elected a fellow of the Australian Academy of Science

Australian Academy of Science

The Australian Academy of Science was founded in 1954 by a group of distinguished Australians, including Australian Fellows of the Royal Society of London. The first president was Sir Mark Oliphant. The Academy is modelled after the Royal Society and operates under a Royal Charter; as such it is...

. In 1992, he was appointed full professor, and in 1999 he started the Key Centre for Polymer Colloids, funded by the Australian Research Council

Australian Research Council

The Australian Research Council is the Australian Government’s main agency for allocating research funding to academics and researchers in Australian universities. Its mission is to advance Australia’s capacity to undertake research that brings economic, social and cultural benefit to the...

, the University and industry. He has served in leadership roles in the International Union of Pure and Applied Chemistry (IUPAC)

International Union of Pure and Applied Chemistry

The International Union of Pure and Applied Chemistry is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science . The international headquarters of IUPAC is located in Zürich,...

, the world ‘governing body’ of chemistry. He was founding chair (1987–98) of the IUPAC Working Party on the Modelling of Kinetics Processes of Polymerisation, of which he remains a member, and is a member of the IUPAC scientific task groups on starch molecular weight measurements, and terminology. He was vice-president (1996–97) and president (1998–2001) of the IUPAC Macromolecular Division, and secretary of the International Polymer Colloids Group (1997–2001). As of 2007, he is Research Professor at the Centre of Nutrition and Food Science, University of Queensland

University of Queensland

The University of Queensland, also known as UQ, is a public university located in state of Queensland, Australia. Founded in 1909, it is the oldest and largest university in Queensland and the fifth oldest in the nation...

, where his research program concentrates on the relations between starch structure and nutrition.

His scientific advances have been based on developing novel theoretical and experimental methods to isolate individual processes in very complex systems. By revealing the mechanistic bases of these individual processes through a combination of theory and experiment, he has significantly deepened, and in some cases revolutionised, the understanding of whole systems in small (gas-phase

Phase (matter)

In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, and chemical composition...

) and giant (polymer

Polymer

A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

) reaction dynamics.

Unimolecular reaction dynamics

Reactions

Reaction mechanism

In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs.Although only the net chemical change is directly observable for most chemical reactions, experiments can often be designed that suggest the possible sequence of steps in...

 in chemical processes are either unimolecular

Molecularity

Molecularity in chemistry is the number of colliding molecular entities that are involved in a single reaction step. While the order of a reaction is derived experimentally, the molecularity is a theoretical concept and can only be applied to elementary reactions...

 or bimolecular. The rate of a unimolecular reaction is an average over a vast ensemble of the rate coefficients for the microscopic events of collisional energy transfer and of reaction of a completely isolated molecule. Gilbert's work in the field of unimolecular processes started with the development of theorems for this relationship. These theorems are elegant developments in matrix algebra

Matrix algebra

Matrix algebra may refer to:*Matrix theory, is the branch of mathematics that studies matrices*Matrix ring, thought of as an algebra over a field or a commutative ring...

, proving relations that had been previously known only for particular cases. His theorems also became the basis for numerical methods that he developed to perform the requisite calculations. For this purpose, he created a computer code, UNIMOL, which is widely used by researchers.

He developed, with Prof J Troe, easily used approximate solutions for the pressure dependence of the rate coefficient. He provided the first solutions for cases where angular momentum conservation needs to be incorporated. His methods are used by experimentalists to fit data and extrapolate to different pressure regimes, supplanting previous tools which were of dubious validity and accuracy. His coworkers and he obtained data on the collisional energy transfer process and used them to prove the conjecture that each collision involves only a small exchange of energy. He then developed the first rigorous means to calculate these quantities from basic theory, and the first physical model for the process. His work is widely used, both for basic understanding of the transition states and by atmospheric and combustion modellers. Predicting climate change

Climate change

Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

 and effects on the ozone layer

Ozone layer

The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 97–99% of the Sun's high frequency ultraviolet light, which is potentially damaging to the life forms on Earth...

 rely critically on this modelling.

Emulsion polymerisation

Emulsion polymerisation is the commonest means of making a wide variety of industrial polymers, such as paints, adhesives and tyre rubber. It is a complex process involving many simultaneous and separate processes and where historically only a few types of data were available. The complexity and the limited data types meant that conflicting assumptions could be forced to agree with experiment: there was no proper understanding of the process. Gilbert developed and applied mathematical and experimental tools whereby the effects resulting from individual processes could be isolated for the first time.

As with unimolecular reactions, the keys to the qualitative and quantitative understanding of the many processes in emulsion polymerisation are the rate coefficients of the individual steps. These steps are initiation (how quickly a growing chain starts), propagation (how quickly individual monomer units are added), radical loss processes (the termination and transfer of radical activity), and particle formation (nucleation). With Prof D Napper, Gilbert applied equations that he had solved in gas-phase chemistry to the area of emulsion polymerisation. This opened the way for him to develop—initially in collaboration with Napper—new theoretical and experimental methods for extracting the rate coefficients of elementary processes. He produced targeted data using these methods, particularly the time evolution of reaction rates and molecular-weight

Molar mass distribution

In linear polymers the individual polymer chains rarely have exactly the same degree of polymerization and molar mass, and there is always a distribution around an average value. The molar mass distribution in a polymer describes the relationship between the number of moles of each polymer species...

 and particle-size distributions. This included novel types of systems, such as γ-radiolysis relaxation, in which events such as radical loss can be separated from radical propagation and growth.

Gilbert's mathematical treatments and experimental techniques revealed the fundamentals controlling these steps by enabling each of the processes to be effectively studied in isolation. His advances allowed rate coefficients to be measured for virtually any process in emulsion polymerisation, values of these rate coefficients for simple systems to be predicted, and the reliability of new measurements to be checked from theory. He used data from applying these methods to obtain the dependence of rate coefficients on controllable quantities, such as initiator concentration. Thus, he tested existing models, developed new tests—some of which refuted extant models—and refined the older models that withstood his tests. At last, it was possible to achieve consistency between supposed microscopic events and experiment, and, for the very first time in the field, to refute postulated models authoritatively.

Using these data, he quantified radical loss from particles, showing that simple diffusion theory could explain the results. Gilbert and his coworkers then revealed the mechanism for initiation in emulsion polymerisation by the entry of radicals into particles—in terms of fundamental thermodynamic and kinetic

Chemical kinetics

Chemical kinetics, also known as reaction kinetics, is the study of rates of chemical processes. Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition...

 precepts—in a theory that clarifies the process as being through production of surface-active species in the water phase. This model produced various qualitative predictions. One prediction, that of the independence of the entry-rate coefficient of the size and surface properties of particles, was widely seen as counterintuitive because of the deep-rooted belief in models that he had shown to be wrong. Subsequently, this prediction was experimentally verified by Gilbert and others. He used the understanding from this knowledge to develop a priori models for particle formation and molecular-weight distribution.

These developments led to a deep understanding of basic processes in free-radical

Radical (chemistry)

Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...

 polymerisation—the commonest industrial process. For the propagation reaction, Gilbert led an international team that produced a methodology that overcame the long-standing problem of obtaining reliable rate coefficients for this process. He showed that the Arrhenius parameters

Temperature dependence of liquid viscosity

The temperature dependence of liquid viscosity is the phenomenon by which liquid viscosity tends to decrease as its temperature increases. This can be observed, for example, by watching how cooking oil appears to move more fluidly upon a frying pan after being heated by a stove...

 for different types of monomer

Monomer

A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...

 take different classes of values, and developed qualitative and quantitative understanding of these classes from fundamental transition-state

Transition state

The transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest energy along this reaction coordinate. At this point, assuming a perfectly irreversible reaction, colliding reactant molecules will always...

 theory and quantum mechanics

Quantum mechanics

Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

. These new methods were based on those that he had developed in his work on unimolecular gas-phase processes. For the termination reaction, his data and models led to the qualitative and quantitative understanding of this process as diffusion-controlled.

Thirty years ago there was neither real predictability nor qualitative understanding of the dominant mechanisms in emulsion polymerisation. Mechanisms had been ‘proved’ by comparing model predictions with experimental data. The data field was limited and the models had many adjustable parameters, or else fitting parameters had values that were subject to wide uncertainty: it was possible to choose values that could suit any model. It was not uncommon to find two papers claiming that quite different mechanisms were dominant in the same system, a result of not being able to isolate the individual steps. As a result of Gilbert’s work, all individual processes in emulsion polymerisation, one of the commonest ways of making everyday products, are now qualitatively and quantitatively understood. It is now possible to polymerise simple systems and to predict the molecular architecture that will be formed under chosen conditions, while for more complex conditions, trends can be semiquantitatively predicted and understood. The international scientific and technical community in this field now uses the mechanistic knowledge that he obtained as the key to understanding current processes and creating new processes and products. His work has put this industrially important field on a rigorous scientific footing.

Gilbert and others have used this knowledge and understanding to develop means of creating new materials. One major example includes his role as leader of a collaborative project that has led to a new generation of surface coatings. He developed the first practical means to implement on industrially significant scales Dr E Rizzardo’s reversible addition-fragmentation chain transfer (RAFT)

RAFT (chemistry)

Reversible Addition-Fragmentation chain Transfer or RAFT polymerization is one kind of controlled radical polymerization. Discovered at the Commonwealth Scientific and Industrial Research Organisation in 1998, RAFT polymerization is a relatively new method for the synthesis of living radical...

 method of controlled radical polymerisation.

Enzymatic processes in starch biosynthesis

In recent research that builds on his work in polymerisation, Gilbert has developed a new way of understanding the biochemistry

Biochemistry

Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...

 of the enzymatic

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 processes involved in starch biosynthesis, in collaboration with Dr Melissa Fitzgerald, International Rice Research Institute

International Rice Research Institute

The International Rice Research Institute is an international NGO. Its headquarters are in Los Baños, Laguna, Philippines, and it has offices in sixteen countries...

, Manilla. In this new field, he applied the methods he had developed for understanding molecular-weight distributions in synthetic polymer

Synthetic polymer

Synthetic polymers are often referred to as "plastics", such as the well-known polyethylene and nylon. However, most of them can be classified in at least three main categories: thermoplastics, thermosets and elastomers....

s to understanding those of natural ones. He has thus created a powerful new technique for probing the enzymatic processes in starch

Starch

Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

 biosynthesis

Biosynthesis

Biosynthesis is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products. The biosynthesis process often consists of several enzymatic steps in which the product of one step is used as substrate in the following step...

in grains, again, creating a methodology to obtain reliable mechanistic knowledge by isolating steps in highly complex systems. Each enzymatic step that creates individual chains—analysed by debranching the starch—can now be associated with particular regions in the molecular-weight distribution of a starch. This supported the applicability of one of two rival mechanistic postulates made by starch biochemists. He has also recently developed a major innovation for solving the vexed problem of quantitatively interpreting data for branched systems.

Selected publications

• "Theory of thermal unimolecular reactions in the fall-off range. II. Weak collision rate constants". RG Gilbert, K Luther, J Troe, Ber Bunsenges Phys Chem, 87, 169–77 (1982)

(How the pressure dependence of a major class of chemical reactions can be fitted and extrapolated; widely used in atmospheric and combustion modelling.)

• Theory of unimolecular and recombination reactions. RG Gilbert, SC Smith. Oxford: Blackwell Scientific Publications (1990), 364 pp

(Set out a major process in chemical kinetics, including many of his discoveries.)

• "Critically evaluated rate coefficients for free-radical polymerization. 1. Propagation rate coefficients for styrene". M Buback, RG Gilbert, RA Hutchinson, B Klumperman, F-D Kuchta, BG Manders, KF O’Driscoll, GT Russell, J Schweer. Macromol. Chem. Phys., 196, 3267–80 (1995) (authors in alphabetical order)

(One of a series of papers from an IUPAC Working Party that Gilbert created and led, which established reliability criteria for what is now a widely used technique for measuring the propagation rate coefficient that controls the speed of polymer growth.)

• "The entry of free radicals into latex particles in emulsion polymerization". IA Maxwell, BR Morrison, DH Napper, RG Gilbert, Macromolecules, 24, 1629–40 (1991)

(Discovery of the mechanism of an important process in this major industrial process.)

• Emulsion polymerization: a mechanistic approach. RG Gilbert. London: Academic Press (1995), 362pp

(Basic mechanisms in this major industrial process, including many of his discoveries.)

• "Molecular weight distributions in free-radical polymerizations. Understanding the effects of chain-length-dependent termination". PA Clay, RG Gilbert. Macromolecules, 28, 552–69 (1995)

(How microscopic events govern a major determinant of properties in this widely used process.)

• "A priori prediction of propagation rate coefficients in free radical polymerizations: propagation of ethylene". JPA Heuts, RG Gilbert, L Radom. Macromolecules, 28, 8771–81 (1995)

(How the sizes of rate coefficients for polymer growth can be understood in terms of basic quantum mechanics.)

• "Pulsed-laser polymerization measurements of the propagation rate coefficient for butyl acrylate". RA Lyons, J Hutovic, MC Piton, DI Christie, PA Clay, BG Manders, SH Kable, RG Gilbert. Macromolecules, 29, 1918–27 (1996)

(The first measure of the propagation rate coefficient for a widely used monomer, showing that it is 100 times faster than previously assumed; now used for the improved design of certain manufacturing processes.)

• "Effective ab initio emulsion polymerization under RAFT control". CJ Ferguson, RJ Hughes, BTT Pham, BS Hawkett, RG Gilbert, AK Serelis, CH Such. Macromolecules, 35, 9243–45 (2002)

(How a new technique of making polymers can be implemented in the commonest industrial manufacturing process; the basis of a new generation of paints soon to be on the market.)

• "Mechanistic information from analysis of molecular weight distributions of starch". JV Castro, C Dumas, H Chiou, MA Fitzgerald, RG Gilbert, Biomacromolecules, 6, 2248–59 (2005)

(How molecular weight data on starch can be plotted to reveal biosynthetic pathways and structure–property relations.)

Patents

• CJ Ferguson, RJ Hughes, BTT Pham, BS Hawkett, RG Gilbert, AK Serelis, CH Such. Aqueous dispersions of polymer particles. PCT/AU02/01735 (2002)

• S Peach, BR Morrison, RG Gilbert. Finely divided polymer dispersions, their production and use. Ger. Offen. DE 19929395 (2000)

• N Subramaniam, R Balic, RG Gilbert. Modified rubber polymer latex. PCT/AU98/00191 (1998)

• D Kukulj, TP Davis, RG Gilbert. Polymerization reactions under miniemulsion conditions. PCT PN6696 (1997)